1. Field of the Invention
The present invention relates to a submerged motor pump of the type in which a motor is installed inside an outer casing such as to define an annular passage therebetween and a pumped liquid is discharged to the outside through the annular passage while cooling the entire periphery of the motor, the motor pump being suitably used as a portable pump for draining water from a pit.
2. Description of the Prior Art
FIG. 1 shows a typical conventional submerged motor pump of the type described above. A motor 1 and a pump casing 3 which incorporates an impeller 2 are connected together as one unit to define a motor pump body. The motor pump body is surrounded by an outer casing 4. The upper end of the outer casing 4 is formed integral with a cover plate 4a having a discharge port 5. A bottom plate which also serves as a strainer 6 is secured to the lower end of the outer casing 4. In the figure, the reference numeral 7 denotes a motor head cover, while the numeral 8 denotes a protective resilient ring which serves as a cushioning member.
In pumping operation, a liquid which is sucked in through the strainer 6 is pressurized by means of the impeller 2 inside the pump casing 3, discharged into the space defined between the outer casing 4 and the motor pump body and then discharged to the outside while cooling an outer casing of the motor 1 through the discharge port 5.
Referring next to FIG. 2, which is a sectional view of another prior art, an outer casing 4 which is formed from a thin metal plate is mounted in such a manner as to be clamped between a motor head cover 7 made of a rigid material and a pump casing 3 which is formed from a resilient material reinforced by a metal core 3a. The upper and lower end portions of the outer casing 4 are engaged with the motor head cover 7 and the pump casing 3 through resilent seal members (boots) 101, respectively, thereby preventing leakage of pumped liquid through the joints.
In this prior art, the upper side of the resilient pump casing 3 is covered with an intermediate casing 9 which is made of a rigid material and these two casings 3 and 9 are fastened together by means of a plurality of bolts 102 (only one is shown). The intermediate casing 9 is fastened to the underside of the motor 1 by means of a plurality of bolts 103 (only one is shown). The head 103a of the bolt 103 is received in a recess 9a which is provided on the underside of the intermediate casing 9. In the figure, the reference numeral 2 denotes an impeller, 3b a fluid passage also serving as a strainer which is formed in the bottom portion of the pump casing 3, 3c a pump casing discharge port, and 5 a pump discharge port.
The above-described conventional submerged motor pumps (those shown respectively in FIGS. 1 and 2) suffer, however, from the following problems.
In the prior art, the pump casing 3 and the outer casing 4 are produced as discrete members and the outer casing 4 is formed using a thin metal plate, e.g., a thin iron plate, with a view to reducing the weight of the machine.
However, the outer casing 4 must have a sufficient thickness to prevent deformation due to external forces, for example, any impact applied thereto during transportation. In actuality, however, the tickness of the outer casing 4 is reduced because priority is given to the desire for a reduction in weight. Accordingly, the outer casing 4 is readily deformed when subjected to external forces.
Since the pump casing 3 and the outer casing 4 are formed as separate members from a metal, the structure of the motor pump is complicated and the bulk densities of materials used to form the motor pump are relatively high, which results in an overall increase in weight.
In the prior art (shown in FIG. 2) wherein the upper end portion of the outer casing 4 made of a thin metal plate and the lower end portion of the motor head cover 7 are engaged with each other through the grooved seal member (boot) 101 made of a resilient material, sealing effect is achieved by pressing the resilient seal member 101 predominantly in the axial direction.
However, if such a grooved seal member (boot) 101 is applied to a pump which has an outer casing 104 made of a resilient material, as shown in FIG. 3(a), when internal pressure P is applied to the outer casing 104, it may be deformed both radially and axially, as shown in FIGS. 3(b) to 3(d), and the sealing performance will thus deteriorate or become nullified. In the case where the resilient outer casing 104 is engaged directly with the lower end portion of the motor head cover 7 without using the above-described resilient seal member, as shown in FIG. 4(a), and, when internal pressure P is applied to the casing 104, a gap is produced at the area of contact between the two members, as shown in FIG. 4(b), resulting in a deterioration of the sealing performance.
In the prior art (shown in FIG. 2) wherein the upper side of the pump casing 3 made of a resilient material reinforced by the metal core 3a is covered by the intermediate casing 9 made of a rigid material, the pump casing 3 and the intermediate casing 9 are fastened together by means of the bolt 102. In the case where a pump bottom plate 105 is secured to the bottom of the resilient pump casing 3, as shown in FIG. 5(a), the resilient pump casing 3 is clamped at the upper and lower sides thereof by the rigid intermediate casing 9 and the pump plate 105, respectively, and these members are fastened together by means of a through-bolt 102 which is passed therethrough from the lower side thereof through a spacer 106 which defines the interference of the resilient pump casing 3.
In this case, however, the number of parts required to fasten the above-described members together increases, and it is difficult to align the intermediate casing 9, the pump casing 3 and the pump plate 105 with each other.
In the case where a stud bolt 102b which has been previously threaded into the intermediate casing 9 is passed through the resilient pump casing 3 and the pump plate 105 with the spacer 106 interposed therebetween and then these members are fastened together by means of a nut 102d which is screwed onto the bolt 102b from the lower side, as shown in FIG. 5(b), alignment of the intermediate casing 9, the pump casing 3 and the pump plate 105 is facilitated, but the number of parts required is even larger than in the case of the arrangement shown in FIG. 5(a).
In the case where a special double-end stud bolt 102c which defines the interference of the resilient pump casing 3 is threaded into the intermediate casing 9 in advance and passed through the pump casing 3 and the pump plate 105 and these members are fastened together by means of a nut 102d which is screwed onto the bolt 102c from the lower side, as shown in FIG. 5(c), the number of parts required is relatively small and the alignment is facilitated. However, this arrangement necessitates employment of the special bolt 102c which is not commercially available.
In the prior art (shown in FIG. 2) wherein the upper side of the resilient pump casing 3 is covered with the rigid intermediate casing 9, the head 103a of the bolt 103 that is used to fasten the intermediate casing 9 to the underside of the motor 1 is received in the recess 9a provided on the underside of the intermediate casing 9. Accordingly, the intermediate casing 9 must be sufficiently thick to ensure the required strength which results in an increase in weight and it also makes it difficult to turn and drive the bolt 103 in the recess 9a.